The long term goal of this proposal is to analyze the mechanisms that maintain the stem cell character of the embryonic germline in C. elegans. The proposed research will characterize the function of the gene pos-1. pos-1 activity is required to prevent the embryonic germ precursors from adopting somatic fates and also for the proper development of posterior somatic blastomeres. The pos-1 mRNA is maternally supplied to the oocyte and is localized to the posterior of the embryo prior to the first embryonic cleavage. The POS-1 protein is first expressed at the 2-cell stage of embryogenesis in the germ precursor and is subsequently present at high levels in the succeeding germ precursors and at low levels in their somatic sisters. The POS-1 protein contains two copies of a zinc finger-like motif of unknown function. This same protein motif is also found in the proteins encoded by the pie-1 and mex-1 genes. These two genes are also required for the development of the germ precursors in C. elegans. The proposed research will determine of pos-1 is required for translational and transcriptional differences between the germ and the soma, and will examine the significance of the presence of POS-1 protein in germ specific structures called P. granules.